This invention relates generally to erasable marking compositions, and more specifically, to water-based, erasable marking compositions containing polyurethane.
It is often desirable to produce ink images from a pen, marker, printer, or other application device which can be readily removed or erased. Typical among these inks were compositions comprising a pigment and a liquid carrier or binder in which the pigment was dispersed. A common water-based erasable ink contained pigment in conjunction with styrene butadiene rubber (SBR) dispersions to provide erasability.
Some typical SBR based inks are disclosed in U.S Pat. No. 5,389,717 to Santini et al., U.S. Pat. No. 5,599,853 to Loftin, U.S. Pat. No. 4,686,260 to Lindemann et al., and U.S. Pat. No. 4,596,846 to Bohne et al.
SBR based inks, however, had drawbacks. SBR based inks often became permanent over time as oxidation caused crosslinking to occur within the composition after it was applied to a substrate. It was observed that as this crosslinking occurred over time, the erasability of the SBR based ink diminished. With enough time (on the order of weeks), the SBR based ink often became essentially unerasable.
Another potential drawback was that SBR based inks, when first applied, were actually too erasablexe2x80x94meaning they smeared and were easily accidentally removed from the paper or surface to which they were applied. These inks also often formed a build-up on the writing nib (e.g. pen point) which usually resulted in an undesirable and unclean writing nib which would smear and apply ink unevenly.
One potential solution to the nib build-up problem was addressed through the use of expensive shaker balls and valve systems. These, although partially improving upon the nib build-up problem, were expensive and still did not solve the other problems.
Solutions were sought to the above problems and included the introduction of antioxidants into the ink composition to prevent oxidation, subsequent crosslinking, and the resultant undesirable impact on erasability. The introduction of these antioxidants extended the period of time one had to erase the ink, but even then often only out to about one month from the time of application.
Attempts have been made to add glycerin to the SBR inks in order to prevent build-up of the ink on the writing nib. The introduction of glycerin was seen, however, to negatively impact the ink erasability and often made the erasure very dirty and left visually unpleasant smudges and smears.
Still other attempts have involved the use of certain inks in combination with specialized surfaces in order to achieve some degree of erasability. Such combinations are disclosed in, for example, U.S. Pat. No. 5,217,255 to Lin et al., U.S. Pat. No. 4,940,628 to Lin et al., and U.S. Pat. No. 4,988,123 to Lin et al. These patents all require that the inks disclosed as erasable be used with certain writing surfaces so as to be erasable. U.S. Pat. No. 5,217,255, for example, teaches that the ink, in order to be satisfactorily erasable, be applied to a surface having an average pore diameter of between about 0.05 and 1.0 microns. Where the substrate does not have such an average pore diameter, it can be treated in order to achieve that range of porosity. Thus, these patents teach ink/substrate systems which provide a degree of erasability.
The drawbacks discussed above suggest the need for a water-based composition that flows well through the writing nib (in the case where the composition is to be used in a pen or marker), does not easily smudge, but which is easily and effectively erased from any surface to which it is applied. Another desirable aspect to such an improved composition would be the length of time it remains easily and effectively erasable after it is initially applied.
The present invention provides a water-based, erasable marking composition comprising water, pigment, glycerin, and polyurethane. The composition may optionally include a surfactant. The ink composition of the present invention is a water-based ink composition that flows well through the writing nib (in the case where the composition is to be used in a pen or marker), does not easily smudge, is easily and effectively erased from the surface to which it is applied, and remains easily and effectively erasable from the surface to which it is applied for an indefinite length of time after it is initially applied to that surface. Also included in the present invention is an application instrument that uses the erasable composition of the present invention.
The water-based, erasable marking composition comprises 1-86% by weight water, 0.3-38% by weight pigment, 13-45% by weight polyurethane, and 0-85% by weight glycerin, wherein the polyurethane has a viscosity which increases by at least a factor of 10 when the polyurethane is in an aqueous dispersion which is dried from a 30% dispersion of polyurethane in water to a 65% polyurethane dispersion in water. The composition optionally includes surfactants and anti-microbial preservatives. The preferred surfactant is a fluorosurfactant.
A more preferred embodiment comprises 13-69% by weight water, 5-15% by weight glycerin, 0.3-6% by weight pigment, and 26-42.5% by weight polyurethane, where the polyurethane is one which has a viscosity that increases by at least a factor of 10 when the polyurethane is in an aqueous dispersion which is dried from a 30% dispersion of polyurethane in water to a 65% polyurethane dispersion in water.
The most preferred embodiment comprises 52% by weight water, 9% by weight glycerin, 4% by weight pigment, and 35% by weight polyurethane, where the polyurethane is one which has a viscosity that increases by at least a factor of 10 when the polyurethane is in an aqueous dispersion which is dried from a 30% dispersion of polyurethane in water to a 65% polyurethane dispersion in water.
The invention also includes an application instrument comprising an outer body, an applicator, a reservoir included within the outer body and in fluid communication with the applicator, and a water-based, erasable marking composition within the reservoir. The water-based, erasable marking composition is that disclosed herein.